Double ended perforated paper roll with plastic film laminations



May 30, 1967 J. H. NICHOLAS 3,322,884 DOUBLE ENDED PERFORATED PAPER ROLL WITH PLASTIC FILM LAMINATIONS Filed July 1, 1966 4 Sheets-Sheet 1 [720672 Jamaflf/Vz'c/wm 5 Jan M440 y 1967 J H. NICHOLAS 3,322,884

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. DOUBLE ENDED PERFORATED PAPER ROLL WITH PLASTIC FILM LAMINATIONS Filed July 1, 1966 y 30, 1967 J H. NICHOLAS 3,322,884

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United States Patent 3,322,884 DOUBLE ENDED PERFORATED PAPER ROLL WITH PLASTIC FILM LAMINATIONS James H. Nicholas, Flossmoor, Ill., assignor to G & W Electric Specialty Co., Blue Island, Ill., a corporation of Illinois Filed July 1, 1966, Ser. No. 562,346 7 Claims. (Cl. 174-73) The invention relates to electric cable terminations and has reference in particular to a stress relief cone that can be produced by the workman on the job from a pre-perforated lamina-ted roll of paper and plastic.

A common means for reducing the electrical stresses at the end of a power transmission cable is to gradually increase the total thickness of the insulation at the terminations by applying a tapered cone of rubber, plastic, varnished cambric, oil impregnated paper or the like. The construction is known as a stress relief cone.

The design of stress relief cones and creepage dimensions of shielded cable terminations are primarily based on two types of dielectric stresses or voltage gradients, namely (1) radial gradients, and (2) axial or longitudinal gradients. The dielectric gradients in a shielded cable are primarily radial. The longitudinal gradients exist by virtue of the creation of a cable end or shield discontinuity and are of the greatest concern at the termination. Radial dielectric gradients also occur at the termination and can be a very important factor especially in the extra high voltage terminations where condenser elements are employed to control the longitudinal dielectric gradients.

Generally, the insulation which can be applied at a cable joint or cable termination is not homogeneous and precise as is true of factory products. Such joints or terminations are made in the field by personnel of varying competence and under a variety of conditions. Hence, the insulation that can be applied in the field leaves much to be desired insofar as dielectric properties in various planes are .concerned. Tests have demonstarted that laminated dielectrics commonly used for cable joints and cable terminations have ratios of as much as thirty to one for the dielectric strengths in radial to longitudinal directions.

The invention provides a stress cone of paper and plastic laminations that can be developed on a cable end in a simple and expeditious manner and with a minimum of equipment and which will make possible the production of such a stress cone on the job and under variable field conditions. The new stress cone will provide an efiicient termination device for high voltage cables since the stress cone geometry can be maintained under accurate and rigid control and wherein the various layers of the laminated material can be coiled into tight contact with adjacent layers.

In general, the stress cone embodying the present invention includes a prewound laminated roll of paper and plastic having accurately controlled lines of cleavage permitting easy removal of excess material in selected areas of the roll so as to shape the roll for its intended purpose.

An addition-a1 object of the invention is to provide a pre-wound roll of laminated paper and plastic having lines of cleavage such as perforations formed for the length of the roll to permit easy removal of the excess material for shaping the roll and wherein the said lines of cleavage are formed in each end portion of the roll, thus making the roll symmetrical about a transverse center line whereby it is possible to place the roll on the cable with either end up or down so that the convolutions of the roll will be either clockwise or counterclockwise.

A more specific object is to provide a pre-wound and pre-perforated paper roll having a plastic film interposed ice between the convolutions of the paper of the roll so that the final stress relief cone will consist of laminations of paper and plastic.

With these and various other objects in view the invention may consist of certain novel features of construction and operation as will be more fully described and particularly pointed out in the specification, drawings and claims appended thereto.

In the drawings which illustrate an embodiment of the invention, and wherein like reference characters are used to designate like parts FIGURE 1 is a view in perspective of an insulating roll embodying the features of the invention, the laminations of paper and plastic being shown as running clockwise;

FIGURE 2 is a view in perspective showing the insulating roll of FIGURE 1 assembled and tightened onto the termination end of a power cable;

FIGURE 3 is a perspective view showing the roll of FIGURE 2 with some paper and plastic laminations being removed along one perforated line;

FIGURE 4 is a view of a partly developed stress relief cone resulting from the removal of excess material as illustrated in FIGURE 3;

FIGURE 5 is a view similar to FIGURE 4 but showing the manner of removing additional paper and plastic laminations along two other perforated lines to develop the ends of the stress relief cone;

FIGURE 6 is another perspective view showing the finished stress relief cone;

FIGURE 7 is a longitudinal section showing the stress relief cone of FIGURE 6 applied to a cable termination Within a pothead;

FIGURE 8 is .a view of a laminated sheet rolled out to show the cleavage lines formed by the perforations;

FIGURES 9- and 10 show a number of equations for the exponential slope and for the straight slope of the completed stress relief cone; and

FIGURE 11 shows a schematic representation of the ectuations of FIGURES 9 and 10.

It will be understood that the stress relief cone will be marketed as a roll 10 of paper and plastic laminations 11 and 12 and ready to be assembled over the terminal end of a power cable such as 13 of predetermined diameter. The power cable consists of a central metal core '14, and conductor shielding tape, a number of layers of insulation, and an outer layer of shielding tape. The outer shielding tape must be removed to expose the cable insulation tapes 16 before the roll 10 is applied.

The tapes 16 may be wound in either a right or a left hand direction, but the operator cannot determine this fact until the outer shielding of the cable is stripped for receiving the stress relief cone. The winding direction of the tapes 16 of the cable core will thus determine the manner in which the roll 10 will be placed on the cable end. That is, with the convolutions of the roll either clockwise or counterclockwise the same as the winding of the tape. For explaining the invention, the tape in FIGURES 1 to 6 is shown as wound clockwise and, therefore, the roll must be placed on the cable end with the convolutions of the same also clockwise. The end 17 of the roll becomes the top end and end 18 becomes the bottom end. In order for the roll 10 to have complete utility in the field the roll can be considered as double ended or in other words the perforations are duplicated at the respective ends 17 and 18.

The paper 11 of the insulation roll 10 may consist of kraft paper or the like such as can be impregnated with oil and the interposed plastic layers may consist of sheets 12 of polyethylene, polypropylene polycarbonate or acetate and the like. The plastic sheets may comprise individual layers between the paper convolutions or the plastic and paper may be bonded to each other and the laminate thus formed is wound to produce the insulation roll.

One series of perforations, namely, the perforations formed in the bottom portion 18 of the roll and the perforations 20a formed in the top portion 17 provide lines of cleavage which will produce the exponentially shaped ends 21 and 21a, FIGURE 6, of the stress relief cone. The other series of perforations, namely, 22 and 22a are provided for producing the straight slope 23, it being understood that the stress relief cone 15 will have only one straight slope and a cylindrical portion 24 between said straight slope and the exponentially shaped end 21a.

The first step in producing the stress relief cone is to remove the outer shielding tape from the cable 13 and maintain the cable in an upright position by suitable means attached to the metal conductor 14. The roll 10 is placed over the cable end and supported in a manner as shown by a temporary support table 25 so that the restraint tabs 26 and 27 are accessible to the workman. While the restraint end tabs are held against the cable, the roll 10 is rotated in the same counterclockwise direction as the cable tape 16 to tighten the roll on the cable. Assuming that the roll has been properly tightened with the ends squared, the outer convolution of the bottom 18 is secured to prevent unwinding. The portion 30 from perforations 22 to the top edge 31 of the roll can now be removed to the diameter of the cylindrical section 24, since this is excess material, thereby forming the straight slope 23 and the cylindrical part 24.

Now with portion 24 being secured to prevent unwinding, the exponentially shaped ends 21 and 21a are developed by removing the strips 32 and 32a. The strip 32 extends from the perforations :20 to the bottom edge 34 whereas the strip 32a extends from the perforations 20a to the top edge 31. The temporary support 25 is removed, and suitable shielding tapes are applied to the lower exponentially shaped end 21 to complete the stress relief cone construction.

Several layers of insulating tape may be applied over the entire structure for dielectric purposes and suitable support of the stress cone obtained by binding a number of metal straps around the circumference of section-21 to form a nest and prevent the roll from slipping down in service.

FIGURE 8 shows a sheet of the laminate material when stretched out flat and which is a development of the stress cone structure. In such a development, the sheet must have a shape as regards the perforated lines that when tightly wound and with certain excess portions being removed the desired shape for the stress cone can be generated. The thinner the sheet material the more pracise will be the control over the exact shape of the final conical surfaces. The thickness of the sheet will provide a step which is straight up and out from the axis of the cone. The superimposed layers of paper and plastic making up the finished stress cone will thus consists of a number of steps. By having the sheet thickness small, the stepped nature of the conical surfaces can be reduced to a point where the individual steps are for all practical purposes negligible and the surface of the cone may then be considered as having a generally continuous slope along the axis.

The sheet of paper 11 may have a thickness of no more than about .020 inch nor less than about .001 inch. In practice a sheet of about five or six mils has been found to be quite desirable. For the plastic sheet 12 the thickness may range from 1 mil to four mils. High voltage cable paper of a thickness of .003 inch and coated with polypropylene of about .005 inch in thickness is commercially available and has been found to be satisfactory for the purposes of the present invention. The sheet material should be flexible enough so that it can be rolled around a cable. Also, the material should not stretch very much during the application of the roll as described- The material 11 as shown in FIGURE 8 has side edges 31 and 34 and the distance between the same determines the length of the stress relief cone. The distance between the inner and outer ends 35 and 36 determines the length of the sheet and which will vary depending on the size of the relief cone to be developed by the roll.

Assuming that the stress relief cone has its axis vertical then y, the radius of a cone section at height x, FIGURE 11, at either of the exponentially sloped ends is given by Equation 1, FIGURE 9, where E is nominal line to ground potential, g is the longitudinal potential gradient in volts per mil, Ln is the natural logarithm, r is the radius of the cable and r is the radius of the outer surface of the cable insulation. At the start end of the slopes 21 and 21a, y is equal to r so that the expression in brackets reduces to l. The logarithm of 1 is zero. As y increases in value above r the expression in brackets grows larger. It is clear that y increases exponentially with respect to x and the stress cone at each end is seen in longitudinal section as concave toward the cone axis. Equation 2 or an approximation thereof will define the line of the perforations 20 and 20a when the sheet is stretched out straight.

For the straight slope the line of perforations is a straight line from beginning to end as clearly evident from the perforations 22 and 22a. However, to determine the value of y which is the radius of the straight cone section at height x FIGURE 11, reference is made to Equation 1 FIGURE 10.

It will also be observed from the schematic showing of the stress relief cone as illustrated in FIGURE 11, that two end slopes of exponential curvature can be developed in addition to two straight slopes, although one straight slope is removed in order to form the cylindrical portion 24. Also, in order to develop said cylindrical portion a part of the exponential slope at one end of the stress relief cone is removed so that the slope 21a is considerably less in extent than the end slope 21. Should the roll 10 be reversed on the cable then the slope 21 would be less in extent than the end slope 21a, the latter being fully developed to provide the bottom end of the stress relief cone. Considering both series of perforations 20 and 22, an approximation may be obtained by plotting a number of separate points and connecting the points by straight lines or shallow curves. Thus when the sheet is rolled up and the excess portions or strips are removed by tearing along the perforated lines, the resulting stress cone will have a surface which can approximate as closely as desired the theoretical surface dictated by mathematical analysis.

In FIGURE 7 the stress relief cone of the invention is shown in applied relation to a cable termination within a pothead. The porcelain body portion 40 is suitably supported from the base or platform 41 by the cylindrical part 42. Said cylindrical part is sealed to the platform 41 and the part is also sealed at 43 to the porcelain body portion. The opposite end of the pothead structure is sealed by the cap 44 so that oil or other liquid can be maintained within the pothead under pressure. It has been previously mentioned that the potential gradients have strong longitudinal components along the non-shielded length of the cable. This is also true at the maximum diameter end of the straight slope 23 where the field applied shielding over the exponential slope 21 is terminated. Accordingly, it is preferred practice in pothead termination structures to employ a stress control member 45 of porcelain or the like and which is cored so as to accommodate the straight slope 23 and the cylindrical part 24.

The shape of the stress relief cone is not limited to that shown in the drawings. In a number of applications, and particularly above the 161 kv. class, the stress relief cone would consist of the the log tapered ends with no straight taper section. The section between the two tapered ends would be cylindrical. No bulge would exist to fit the porcelain member 45, since in these cases no porcelain member such as 45 is needed.

One of the important advantages of the laminated paper and plastic relief cone is the reduction in the specific inductive capacitance, lower dielectric loss and increased radial dielectric strength which is obtained. The extra high voltage cables will probably utilize tapes of plastics instead of paper to reduce the dielectric losses in the cable. The use of oildmpregnated paper rolls on such insulated cables would result in dielectric mismatch, in addition to having the relatively higher dielectric losses. Another advantage resides in the fact that the paper and plastic relief cone is well suited for extruded plastic insulated power cables.

Although an all plastic relief cone would more clearly duplicate the dielectric and physical characteristics of the cable insulation, it is not possible to guarantee a void-free interface between adjacent layers of film. When, a layer of plastic film is interposed between the paper convolutions and the whole is impregnated with a dielectric fluid, the paper has a natural cushioning effect and the operation of the whole roll in a pressurized liquid environment is substantially void free. Also the paper has a natural wicking action for the replenishment of any liquid that may be squeezed out by thermal cycle action. Thus the paper-plastic laminate is a compromise between that which would be desirable from a dielectric point of view and that which is functionally needed.

What is claimed is:

1. An article of manufacture comprising a roll of flexible sheet material formed of paper and plastic laminations and having perforations therein to form weakened lines of cleavage, said weakened lines of cleavage being duplicated in the half sections of the sheet on the respective sides of a longitudinal center line, said weakened lines of cleavage comprising two lines in each half section of the sheet only one of which extends for the full length of the sheet, and said weakened lines of cleavage permitting separation of certain selected areas of the laminated sheet material whereby to so shape the exterior surface of the roll as to form a stress relief cone.

2. An article of manufacture as defined by claim 1, wherein the laminated sheet material consists of paper capable of being impregnated with oil and having negligible stretch along the length of the sheet anda thickness ranging from .001 to .020 of an inch, and a plastic layer preferably bonded to the paper and having a thickness ranging from .001 to .008 inch.

3. An article of manufacture comprising a roll of laminated sheet material consisting of paper and plastic laminations, said roll having utility as a stress relief cone for an electric cable, said r-oll having the ends thereof substantially even resulting from the use of sheet material having substantially constant width, said sheet of laminated material having perforations therein to form weakened lines of cleavage and which are duplicated in the half sections of the sheet on the respective sides of a longitudinal center line, said weakened lines of cleavage comprising two lines in each half section of the sheet only one of which extends for the full length of the sheet, and said weakened lines of cleavage permitting separation of certain selected areas of the laminated sheet material between the weakened lines of cleavage and a longitudinal edge of the sheet, whereby to so shape the exterior surface of the roll as to form a stress relief cone.

4. An article of manufacture as defined by claim 3, wherein the inner edge portion of the laminated sheet material has at least one tab extending beyond the end of the roll, said tab being sufficiently large to be grasped by a workman for holding the inner convolution of the roll from turning while the roll is being rotated to tighten the roll on the said cable core.

5. An article of manufacture as defined by claim 3, wherein the laminated sheet material consists of paper capable of being impregnated with oil and a plastic coating for the paper and which is bonded thereto.

6. An article of manufacture as defined by claim 3, wherein the lines of cleavage which extend for the full length of the sheet are defined by an equation which states that the distance between each said line and an adjacent longitudinal edge of the sheet is a continuous function of the distance from the inner end of the sheet.

'7. A stress relief cone for an electric cable, said cone being formed of convolutions of paper with a plastic sheet being interposed between the convolutions, and said cone having a conical portion at each end, the exterior surfaces of which slope exponentially, a conical portion of straight slope in back to back relation with respect to one of said conical portions of exponential slope, and a cylindrical portion extending from the end of the conical portion of straight slope to the start of the other exponentially sloped conical portion.

LARAMIE s. ASKIN, Primary Examiner, 

1. AN ARTICLE OF MANUFACTURE COMPRISING A ROLL OF FLEXIBLE SHEET MATERIAL FORMED OF PAPER AND PLASTIC LAMINATIONS AND HAVING PERFORATIONS THEREIN TO FORM WEAKENED LINES OF CLEAVAGE, SAID WEAKENED LINES OF CLEAVAGE BEING DUPLICATED IN THE HALF SECTIONS OF THE SHEET ON THE RESPECTIVE SIDES OF A LONGITUDINAL CENTER LINE, SAID WEAKENED LINES OF CLEAVAGE COMPRISING TWO LINES IN EACH HALF SECTION OF THE SHEET ONLY ONE WHICH EXTENDS FOR THE FULL LENGTH OF THE SHEET, AND SAID WEAKENED LINES OF CLEAVAGE PERMITTING SEPARATION OF CERTAIN SELECTED AREAS OF THE LAMINATED SHEET MATERIAL WHEREBY TO SO SHAPE THE EXTERIOR SURFACE OF THE ROLL AS TO FORM A STRESS RELIEF CONE. 